Field of Invention
The present invention relates to a charging circuit, particularly to a current scale-up charging circuit. The present invention also relates to a capacitive power conversion circuit and a charging control method for use in the charging circuit.
Description of Related Art
FIG. 1 shows a prior art charging circuit (charging circuit 1) which comprises an adaptor 11 capable of directly charging a battery 50. The adaptor 11 can provide a charging current IBAT through a cable 20 (for example a USB cable) and a load switch 40 to the battery 50 for charging the battery 50 by a constant current. However, when using a USB standard cable, the maximum current is limited by the cable current rating, which is 5 A or lower, and therefore a longer charging time is required. If it is desired to raise the charging current, for example to 8 A or higher to expedite the charging time, a specially-designed fast charging cable with a larger diameter is required. However, it is inconvenient to use the fast charging cable, because first, it is a non-standard cable, and second, the fast charging cable is less flexible for accommodation due to its larger diameter.
FIG. 2 shows a prior art charging circuit (charging circuit 2) which includes a switching conversion circuit 60 which can convert the power provided by the adaptor 11 (for example but not limited to 5V, 9V, or 12V VBUS of USB PD) to a charging current IBAT to charge a battery 50 by a constant current. The prior art circuit in FIG. 2 has a drawback that it is very difficult to optimize the choices of the specifications of the inductor and switches (both not shown) of the switching conversion circuit 60 so that critical parameters such as the charging current, current ripple amplitude, conduction resistance of the switch, power conversion efficiency and etc. can be optimized.
Compared to the prior art in FIG. 1, the present invention is advantageous in providing a scale-up charging current for charging a battery to shorten the charging time, while a standard cable such as a USB compliant cable can be used, through which only a relatively lower current is allowed. Compared to the prior art in FIG. 2, the present invention is advantageous in not requiring an inductor, having a smaller size, lower cost, and easier optimization for component selections to maximize power conversion efficiency.